Nebulizers for producing micro-droplets (i.e. aerosol) from liquid medicaments and presenting those aerosols for patient respiratory therapy are a well-known and practiced technology. A typical nebulizer design includes the basic elements of a gas inlet port, a respirable gas outlet, a liquid reservoir and a means for forming micro-droplets of the liquid within the reservoir. Early designs, such as represented by U.S. Pat. No. 3,097,645 and U.S. Pat. No. 3,762,409, both to Lester and incorporated by reference in their entireties herein, depict the basic elements of a typical constant-flow type nebulizer. Constant-flow type nebulizers create micro-droplets of liquid medicament based on an uninterrupted supply of pressurized gas coming through the gas inlet port and entraining liquid from the reservoir continually, forming a fraction of the liquid into an aerosol until such time the pressurized gas is stopped or the reservoir of liquid becomes empty. While representative simple nebulizers such as taught by Lester are capable of producing an aerosol, the efficiency of simply jetting an entrained liquid stream into a free space was not found to be adequate for creating micro-droplets of a consistent size and rate. U.S. Pat. No. 4,588,129 to Shanks, incorporated herein by reference in its entirety, addresses this consistent size and rate issue of the earlier Lester designs by further incorporating a fixed baffle having a convex target surface. In the Shanks nebulizer, a liquid entrained jet stream strikes upon the convex target surface of the baffle and the impact thereof allows for the momentum imbued within the liquid stream to mechanically act upon the stream and cause the creation of smaller, more readily inhaled micro-droplets at a higher rate.
The Lester and Shanks nebulizers greatly advanced the art of aerosol formation, however, due to their continuous aerosol formation mode of operation, much of the liquid medicament formed into an aerosol was lost from the device during patient exhalation and idle operation of the device. Loss of aerosolized medicament to the environment is deleterious as there is a decrease in therapeutic value to the patient resulting from reduced dosing, as well as, contamination of the immediate atmospheric environment and inadvertent dosing of individuals not requiring treatment. Dosing variability with continuous aerosol formation nebulizers is also very high and largely affected by the physiological respiratory of the patient, thus two different patients with two different inhalation and exhalation time ratios using the same continuous aerosol formation nebulizer will receive significantly different doses. Improvements were then made to alter nebulizer performance such that the creation of micro-droplets through aerosolization occurred only when the patient being treated was inhaling through the nebulizer. Published U.S. Patent Application 2003/0136399 to Foley, et al., teaches a means for a nebulizer, which creates a constant micro-droplet aerosol within a closed chamber, which is released through operation of a valve. Published U.S. Patent Application 2002/0157663 to Blacker, et al., seeks to control aerosol production through patient inhalation completing the path from the liquid reservoir to the entrainment orifice and thereby allow liquid to entrain into the pressurized gas. U.S. Pat. No. 7,080,643 to Grychowski, et al., utilizes a gas diverter, which moves into and out of position wherein pressurized gas is directed across liquid transfer conduits and the vacuum created thereby causes liquid to be drawn through the transfer conduits and entrained into the gas flow. The aforementioned U.S. patent numbers are incorporated herein in their respective entireties.
Although many of the problems of continuous nebulizers has been mitigated by various clinical practices, the nature of medications needed to be aerosolized for inhalation by patient has begun to change such that there is a greater need for control of dosing and environmental exposure. Previously, aerosolized medications were primarily aqueous solutions containing low mass concentrations of salts or other easily soluble compounds with wide allowable dosing profiles and low toxicities. A number of new medication have begun to be introduced, including some consisting of proteins and other biological material, that have much tighter allowable dosing profiles, greater toxicity risks, and greater concern of secondary exposure of un-intended individuals present during treatment due to exposure to exhaled aerosolized medication or aerosolized medication produced at some other time than inhalation. Some of these newer medications tend to have a much higher mass concentrations resulting in thicker solutions and higher viscosities. The result is that much more residual material may be caused to accumulate in or around the nozzle, which can impede or prevent the proper performance of the nebulizer over the course of treatment. Accumulation of material around the nebulizer nozzle, thus impeding performance, is a particular problem with nebulizers that are breath-actuated through means that include intermittently turning on and off gas or liquid flow in synchronization with patient respiration, due to the enhanced drying effect realized by these strategies. Dosing of these medications is many times a much more sensitive issue than older medications, thus a nebulizer that delivers medication only upon inhalation has a distinct advantage over those that run continuously, because inhalation and exhalation time ratios can vary tremendously from patient to patient, thus a breath actuated nebulizer can deliver a more consistent dose regardless of respiration pattern. Furthermore, breath-actuated nebulizers may help mitigate secondary exposure issues by insuring that aerosol is produced only during inhalation, although it is well known that patients will exhale some of the aerosolized medication that has been inhaled and a breath-actuated nebulizer by itself does not completely solve the problem of secondary exposure. Unfortunately, if nebulizer performance is degraded due to accumulation of medication in or around the nozzle, the benefits of breath-actuation can be largely offset by the degraded performance of the nebulizer. Therefore a need exists for a breath-actuated nebulizer that is less sensitive to material accumulation of large molecule medications, that is designed primarily for delivery during patient inhalation, and which has a design that lends itself to mitigation and control of secondary exposure.
Many existing breath-actuated nebulizer involve electrical or sophisticated mechanical components necessary to detect patient inhalation. These devices suffer from high purchase price associated with added sophistication and the inconvenience of a re-usable component that needs to be stored, retained, set up, and cleaned with each use. Therefore a need also exists for a breath-actuated device that is simple in design and capable of being entirely made out of inexpensive parts and therefore potentially for single use and disposable.
The present invention satisfies all of these referenced needs.